This project will examine the changes in calcium content and movement in the mono-oocyte before and during germinal vesicle breakdown in vitro. While a great deal is known about the control of oocyte maturation and ovulation in whole animals, very little is known about the control of the initiation of meiotic maturation at the cellular level in mammals. Our long-term goal is the increased understanding of the physiological mechanisms by which gonadotropins and steroid hormones affect meiosis. Our initial investigations have shown that calcium may be the central intracellular mediator that controls the re-initiation of meiosis. We propose, therefore, to describe the changes in calcium in oocytes during the early stages of meiotic maturation with calcium ion-specific electrodes, radioisotope tracer flux and chlorotetracycline fluorescence. After describing these changes, we will then use treatments that alter calcium movement in an attempt to identify those changes that have regulatory effect upon the oocyte. This approach will identify both specific changes in calcium content or movement, and the cellular mechanisms that cause these changes. This increased knowledge of cellulare mechanisms should lead to increased understanding of the control of meiosis in maammals and the regulation of fertility in general.